The modern automotive vehicle utilizes several cast components that are subject to vibration during vehicle operation. Some of these components, such as the brake rotor, are subject to vibration during braking. Others, such as suspension parts, are subject to vibration during vehicle movement. Still others, such as the vehicle engine block, are subject to vibration at any time the vehicle engine is on.
The disc brake system is particularly subject to vibration and the resulting undesirable noise, vibration and harshness. The conventional disc brake system of today's vehicle incorporates a hydraulically-operated disc brake assembly that includes a brake caliper fixed to the vehicle and a disc brake rotor. The brake caliper includes a pair of opposed brake pads of which one is driven by a piston. The brake disc includes a disc and a central hub. Upon braking, the disc of the disc brake rotor is captured between the opposed brake pads.
The disc brake rotors are key components of a braking system. The rotors are load-carrying elements as they represent half of the disc/pad friction pair. The disc brake rotor is also a very efficient radiator of sound due to its large surface area. Braking action takes place between the rotors and brake pads pushed against the rotor under hydraulic pressure. Under light pressures often used by customers to control vehicle speed, brake pads can make only a partial contact with rotor surfaces leading to unstable friction between the brake pads and the rotor. Unstable behavior of the disc/pad friction pair can cause a resonant vibration in the brake disc. Since grey cast iron material typically used for brake discs has relatively low damping capacity, the disc resonant vibration amplitude might built up to produce objectionable squeal noise. This noise is a significant, recurring, and stubborn source of customer complaints to vehicle manufacturers. The volume and expense of remediation efforts encourage vehicle engineers to seek further improvements on brake systems.
Thus, an increase in the disc brake rotor damping capacity is highly desired to suppress the disc resonant vibration and to prevent squeal noise occurrence. Numerous prior studies have shown that an introduction of coulomb friction damping into a brake disc can help attenuate its resonant vibration and mute the squeal noise. (See, e.g., A. Akay, Acoustics of Friction, J. Acoust. Soc. Am., Vol. 111, No. 4, pp. 1539-1540, April 2002.) Such studies have also shown that contacts that generate friction damping generally fall into two groups: 1) contact between nominally conforming surfaces that do not have a relative rigid-body motion between the surfaces (as in the case of wire cables, e.g., U.S. Patent Pub. No. 20160097433 A1), and 2) contacting surfaces that also have a relative whole-body motion as in the case of solid inserts in brake rotors, e.g. (U.S. Pat. No 7,975,750 B2).
Unfortunately, none of the friction damper proposals using embedded solid inserts have yet been implemented for mass production because of concerns related to the structural integrity of the modified brake rotors. The primary challenge of these proposals includes the need for the insert surfaces to have both an ability of sliding inside the disc plate for friction damping and a proper bonding to the base rotor material to ensure the structural integrity of the rotor. In reality, it is very difficult to always satisfy such contradictory requirements for the same friction interface. For example, U.S. Patent Pub. No. 20130256143 A1, U.S. Pat. No. 8,118,079 B2, and U.S. Pat. No. 8,245,758 B2 proposed pre-treating the insert surfaces to avoid complete bonding with rotor surfaces during casting. However, such pre-treatment can lead to insufficient bonding between the insert and rotor surfaces, which may impact brake rotor structural integrity, representing a safety concern.
To address safety concerns, U.S. Patent Pub. No. 20160097433 A1 proposes the embedding of wire cables into brake components as friction damper inserts where the outer surface of the cable is used for bonding between the cable and the rotor materials while the wires inside are free to slide with respect to each other and thereby provide friction damping.
Other cast components, such as suspension components and the engine block as mentioned above, are subject to vibration during operation. Many of the same problems attributed to the disc rotor arise in these components during vehicle operation. Similar efforts have been undertaken to address these problems as have been undertaken in dealing with vibration in the brake rotor.
However, despite these improvements in the state of the art, there yet remains room in the technology of cast vehicle components for improvements that yield a reduction in noise, vibration and harshness without compromising structural integrity.